Hi there, I have very little to say that would be *good* about Candy Crush Saga, and the book helps explain why, though... it's complicated. I spent more than a decade of my programming career working on games designed to be 'addicting'. I even taught this form of interactive design at UCLA entertainment studies, and it was something I was proud of. But I've done a complete 180° on that, and the Badass book helps explain why.
A game can make money by being 'addictive' but it is never a long-term successful business strategy and I no longer believe it is ethical to do so.
However, there are two ways in which a game can be thought of as 'addictive', and they involve two very different forms of psychology. What we think of as an 'addictive' game like Candy Crush Saga (and virtually all the Zynga games were based 100% on this) is using behavioral psychology based on BF Skinner "operant conditioning", and is driven purely by the addictive impact of 'intermittent variable reward'. (I am also an animal trainer so I know a LOT about this ;)
But there is another form of 'addiction' (though it's not technically using the same addictive pathways in the brain) and it is one EVERY programmer can relate to: the feeling of "I'm just one compile away from this working!!" This is the feeling of "Flow", and the book "Flow: The Psychology of Optimal Experience" was the game designer 'bible' of all the game designers I knew and worked with at Virgin Sound and Vision back in the 90's. It is an experience that causes people to keep doing something, but in a healthy way that has none of the negative side-effects of the behavioral/Skinner version of 'addiction' used by most of the social and FB games we see today (and perfected by things like video slot machines in casinos).
Short answer: you want people to want to engage with a game (or any activity) *because it is enriching their experience and they are building skills and/or knowledge and awareness* and NOT because the game is pushing their reward center buttons to get low level behavior addiction.
My book does explain this, but you can also learn a lot about this just from watching Dan Pink's TED talk "Drive".